1. Field of Invention
The present invention relates to a light-emitting device. More particularly, the present invention relates to an organic light-emitting diode.
2. Description of Related Art
A white-light organic light-emitting diode (WOLED) can be made by a single luminescent layer or multiple luminescent layers. However, the color of the emitting light of the same WOLED varies when the applied operating voltage varies. That is, the wavelength of the emitted light is shifted by applying different operating voltages to the WOLED.
The individual layers of a conventional WOLED are a substrate, an anode (ITO), a hole injection layer (PEDOT:PSS, 40 nm), a hole transfer layer (α-NPD, 40 nm), a blue light-emitting layer ((CF3ppy)2Ir(pic):CDBP, 25 nm)), a hole barrier layer (BAlq, 3 nm), a red light-emitting layer (Ir(btp)2(acac):CDBP, 10 nm), an electron transfer layer (BAlq, 45 nm), an electron injection layer (LiF, 0.5 nm), and a cathode (Al, 150 nm). The red light (600-700 nm) emitting intensity becomes greater as the applied voltage of WOLED is increased (Current Applied Physics 2005, Vol. 5, pp. 331-336). Because of this increasing red shift, controlling the emitting light color of a WOLED is difficult.